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.Dd November 9, 2019
.Dt NTB_HW_PLX 4
.Os
.Sh NAME
.Nm ntb_hw_plx
.Nd PLX/Avago/Broadcom Non-Transparent Bridge driver
.Sh SYNOPSIS
To compile this driver into your kernel,
place the following lines in your kernel configuration file:
.Bd -ragged -offset indent
.Cd "device ntb"
.Cd "device ntb_hw_plx"
.Ed
.Pp
Or, to load the driver as a module at boot, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
ntb_hw_plx_load="YES"
.Ed
.Pp
The following tunables are settable from the
.Xr loader 8 :
.Bl -ohang
.It Va hint.ntb_hw. Ns Ar X Ns Va .b2b
Being set to 1 (default) tells the driver attached to Virtual Interface of the
NTB that it works in NTB-to-NTB (back-to-back) mode, 0 -- NTB-to-Root Port.
Driver attached to Link Interface (visible from Root Port side) switches to
NTB-to-Root Port mode automatically, but one attached to Virtual Interface
can't detect what is on the other side and require external knowledge.
.It Va hint.ntb_hw. Ns Ar X Ns Va .split
Being set above zero splits BAR2 into 2^x memory windows using Address
Lookup Table (A-LUT).
.El
.Sh DESCRIPTION
The
.Nm
driver provides support for the Non-Transparent Bridge (NTB) hardware in
PLX PCIe bridge chips, which allow up to two of their PCIe ports to be
switched from transparent to non-transparent bridge mode.
In this mode bridge looks not as a PCI bridge, but as PCI endpoint device.
The driver hides hardware details, exposing memory windows, scratchpads
and doorbells of the other side via hardware independent KPI to
.Xr ntb 4
subsystem.
.Pp
Each PLX NTB provides up to 2 64-bit or 4 32-bit memory windows to the
other system's memory, 6 or 12 scratchpad registers and 16 doorbells to
interrupt the other system.
If Address Lookup Table (A-LUT) is enabled, BAR2 can be split into several
(up to 128) memory windows.
In NTB-to-NTB mode one of memory windows (or half of it, if bigger then 1MB)
is consumed by the driver itself to access scratchpad and doorbell registers
of the other side.
.Sh HARDWARE
The following PLX/Avago/Broadcom chips are supported by the
.Nm
driver:
.Pp
.Bl -bullet -compact
.It
PEX 8713
.It
PEX 8717
.It
PEX 8725
.It
PEX 8733
.It
PEX 8749
.El
.Pp
, but it may also work with other compatible ones.
.Sh CONFIGURATION
The basic chip configuration should be done by serial EEPROM or via i2c.
It includes enabling NTB on one or both sides (choosing between NTB-to-NTB
(back-to-back) and NTB-to-Root Port modes) and configuring BARs sizes.
.Pp
The recommended mode is NTB-to-NTB mode, since while NTB-to-Root Port is
generally supported by the driver, it require PCI hotplug handling on the
Root Port, that may be difficult or cause different kinds of problems.
.Sh SEE ALSO
.Xr if_ntb 4 ,
.Xr ntb 4 ,
.Xr ntb_transport 4
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written by
.An Alexander Motin Aq Mt mav@FreeBSD.org .
.Sh BUGS
There is no way to protect your system from malicious behavior on the other
system once the link is brought up.
Anyone with root or kernel access on the other system can read or write to
any location on your system.
In other words, only connect two systems that completely trust each other.
